Recently, a hybrid vehicle has been attracting attention as a vehicle that attains both environmental performance and traveling performance. A hybrid vehicle uses, as a power source, a motor driven by a DC power source through an inverter, in addition to a conventional engine. Specifically, a power source is obtained by driving the engine and, in addition, a DC voltage from a DC power source is converted to an AC voltage by the inverter, and a power source is obtained as the motor is rotated by the converted AC voltage.
In most of the currently available hybrid vehicles, the power output device generating the power for driving the vehicle has such a structure that a large, box-shaped case of the inverter is fixed on the chassis, and a motor case (trans axle) is arranged therebelow. Considering a power output device of a hybrid vehicle that can be mounted on as wide a variety of models as possible, a structure having two cases is disadvantageous in component standardization, as the arrangements must be optimized model by model.
In principle, it is desirable to put units that require combined operation into one case for integration. In view of the foregoing, Japanese Patent Laying-Open No. 2004-343845 discloses a drive unit for a hybrid vehicle in which motors and inverters are integrated.
Now, for a hybrid vehicle, an approach of boosting a DC voltage from a DC power source by a boost converter and supplying the boosted DC voltage to the inverter has been proposed. This is to attain higher output of the motor and to improve energy efficiency.
Therefore, it is apparent from the viewpoint of cooperation that, if the boost converter is integrated with the motor as in the case of the inverter, better effect of component standardization and size reduction of the device can be attained.
The drive unit for a hybrid vehicle disclosed in Japanese Patent Laying-Open No. 2004-343845, however, is directed only to a simple structure having the inverter mounted on the motor, and this laid-open application neither discloses nor suggests any structure in which the boost converter is integrated additionally.
The boost converter is generally formed by combining a reactor and a chopper circuit including a switching element. Specifically, to the reactor, a switched current flows from the DC power source dependent on ON/OFF of the switching element, and the power is accumulated. The reactor supplies the accumulated electric power to the inverter side, dependent on ON/OFF of the switching element. The boost converter attains boosting by repeating such an operation.
In the boosting operation, when the switched current flows through the coil of the reactor, vibration occurs due to a magnetic flux circulating through the core. The vibration may possibly propagates to the body, resulting in noise in the vehicle interior. Therefore, in a conventional power output device, separate means for absorbing reactor vibration has been provided (for example, see Japanese Patent Laying-Open Nos. 2005-32830 and 2005-73392).
From the foregoing, when the boost converter is to be integrated with the motor, sufficient consideration must be given not only to the reduction in size of the device but also to the provision of the reactor vibration absorbing means.
Therefore, the present invention was made in order to solve these problems and its object is to provide a power output device of a hybrid vehicle having an integrated motor driving system and capable of absorbing reactor vibration of the motor driving system.